Marine thrusters typically mount on barges and flat boats, and are used as propulsion for these vessels. One type of marine thruster employs a prime mover such as a diesel engine driving a hydraulic pump, together known as a “power pack”, and the resultant pressurized hydraulic fluid may be employed to drive a propeller attached to a lower unit.
There are a number of problems associated with currently available marine thrusters. Where a centrally located tiltable lower unit has been retracted and tilted backwards for storage, maintenance, cleaning, etc., the protruding upper end of the lower unit interferes with the helm and helm platform, and prevents full upward tilting of the retracted lower unit. Therefore, it would be desirable to provide a marine thruster which may be retracted and then fully tilted.
Another problem with current designs is the lack of an effective extension and retraction mechanism for lower units. It is important to be able to retract the lower unit so as to be able to more easily tilt the lower unit upwards for maintenance, storage, or transportation. A number of practical problems must be overcome to provide for an effective retraction apparatus. These include maintaining the angular orientation between cooperating telescoping sections (such as the instant shaft and tube) to allow steering, after the lower unit is extended. Another problem is providing for power assist, so as to avoid the greater work of manually extending and retracting the lower unit. Still another extension/retraction problem lies in adequately supporting the lower end of an extended lower unit, given the long resultant length of the lower unit when extended, and the resultant longer moment arm between the lower unit's mounting point at its upper end, and the propeller's location at its lower end.
Another problem with existing designs: the hydraulic fluid reservoir is disposed on the base of the marine thruster, where it is incapable of supplying enough fluid head to self-prime the power pack, and to facilitate hydraulic fluid flow to the hydraulic power pack. Thus, it would be desirable to provide a hydraulic fluid reservoir which is elevated above the level of the power pack.
Still another problem is where a marine thruster's single lower unit propeller does not supply enough power to adequately propel a vessel upon which it is mounted. It would therefore be desirable to provide a marine thruster with more than one lower unit, for increased power.
Other problems with existing designs include insufficient reinforcement at the lower unit tilt actuator attach point on the base, inadequate bearing surface at the lower unit pivot point, and excess steering motor stress.
Existing Designs
FIGS. 1 and 2 are illustrative of the tilt interference problem, and are rear views of a prior art marine thrusters 2. The location of their lower units 4 directly behind their respective helms causes interference between lower unit 4 and the helm when attempting to fully tilt lower unit 38 up when lower unit 38 is fully retractable. This interference prevents lower unit 38 from fully tilting up when it is fully retracted, thus hindering stowing of lower unit 38 for storage, transportation, servicing, or cleaning.
In addition, the mounting of the hydraulic fluid reservoir on the base of this design provides inadequate flow from the hydraulic fluid tank for self-priming and gravitational flow from hydraulic fluid tank to power pack.